Channel electron multipliers (CEMs) are used to amplify charged particle, photon, or energetic neutral particle signals. CEMs are used to detect photons, charged particles both positive and negative, and energetic neutral particles. They are used as detectors in mass spectrometers as well as in surface analyzers such as auger and x-ray/ultraviolet photoelectron spectrometers, and are also employed in electron microscopes. In addition, they can also be used for electron multiplication in a photon multiplier application.
The CEM makes use of an emissive surface to generate electron multiplication. The emissive surface will emit secondary electrons when struck by a charged particle, or energetic neutral particle, or photon, with sufficient energy. This process is repeated and generates an electron avalanche down the length of the channel. An electron collector, such as a Faraday cup, at the end of the channel collects the electrons and converts them into an electrical pulse.
Typical CEMs are tubular in nature and have an integral funnel cone attached to the input beam end to increase input beam profile detection. CEMs having single and multiple channels in one body have been commercialized. A single channel CEM has a shorter output current dynamic range than a multiple channel CEM having the same channel resistance per channel. The stability and lifetime of CEMs depend on the active emissive surface area. Therefore, a single channel CEM lifetime is shorter. In addition, the single channel CEM high output current operation is less stable than a multiple channel electron multiplier. However, a multiple channel electron multiplier suffers losses in detection efficiency due to an inactive area between the channels at the input beam end. In a single channel electron multiplier, the detection efficiency is maximized due to a smooth transition between the funnel cone and the channel.
There is a need in the art for a CEM providing high detection efficiency and increased lifetime.